The present invention relates generally to spinning aperture radiometers, and more particularly to spinning strip (partial) aperture imaging radiometers that synthesize circular (full) aperture radiometric images from a plurality of rotating strip aperture image measurements.
To provide high resolution images from space-based platforms, for example, conventional sensor architectures incorporate active control of large, heavy, deployable optical systems. Depending upon the mission requirements and the size of the primary mirror, the active control can range from periodic piston and tilt control of primary mirror segments to piston, tilt, figure, and alignment control of all optical elements comprising the sensor.
Full aperture systems with the same resolution as the present invention have a great deal of light gathering capability because of their relatively large aperture areas. However, to place multi-meter diameter apertures into orbit, full aperture systems competing with the present invention require: segmented optical surfaces and folded support structures, if the optical system diameters are larger than the launch vehicle's fairing; complex and potentially high bandwidth adaptive optical techniques, if thin deformable mirrors are used to save weight; and complex piston and pupil matching control, if implemented as a phased array. Therefore, the full aperture systems are relatively heavy and have high technical risk when compared to the present invention.
The closest prior art relating to the present invention is disclosed in U.S. Pat. No. 4,724,439 entitled "Microwave Radiometer Using Fanbeam Inversion" issued to Wiley et al., and assigned to the assignee of the present invention. The invention taught in that patent is generally known as the "SPINRAD" system. The commonality of the approaches between the SPINRAD system and the system of the present invention (referred to as SPINAP) arises from the use of temporally registered strip aperture measurements to synthesize the equivalent full aperture image.
However, the SPINRAD system makes use of only one dimensional spatial frequency information from each of its' equivalent strip aperture measurements, and as such requires fine resolution line of sight control. Furthermore, the SPINRAD system provides for imaging in the microwave frequency region only.
Therefore, it would be an advantage to have a system and image processing method that provides a low risk, low cost, light weight, and simple fabrication and deployment alternative to deploying complex, large aperture, adaptive optical systems for space-based imaging applications.